1. Field of the Invention
The present invention relates generally to a roller skate steering and suspension mechanism, and more particularly to a triple action steering and suspension mechanism providing more responsive and durable operation during competitive roller skating.
2. Description of the Prior Art
Roller skate steering and suspension mechanisms have been in production for over a century. The modern quad roller skate, with a forward pair of wheels and a rear pair of wheels, generally has each pair of wheels secured to an axle which is mounted in a truck that is pivotally connected to a skate base plate, which is in turn secured to the skate boot or shoe. The trucks provide steering response whereby when a skater shifts weight laterally across the base plate, the truck twists, causing the axle to turn. The forward and rear trucks are mounted oppositely so that the axles will turn in opposite directions, causing the wheels to travel in an arc. The trucks also serve, by means of a resilient suspension system, to resist the skater's lateral tilt of the base plate, thus stabilizing the base plate and returning it to a centered and horizontal position when the turn is completed. Skate trucks generally sacrifice the ability to turn in exchange for lateral stability, thus becoming stiff and unresponsive when tightened sufficiently. Conversely, loosening the trucks for improved turning can lead to mechanical instability. Stiffer skate mechanisms will more efficiently transfer muscle power to skate speed, and are preferred by speed skaters who aren't likely to be making many sudden turns. Additional factors affecting roller skate performance include base plate weight, stiffness and durability, where the ideal roller skate base plate balances the tradeoffs of light weight, high stiffness and sufficient durability.
The steering and the resilient suspension system are generally implemented including a single or a double action mechanism. The single action mechanism has one cushion, usually made of rubber or a urethane compound, that sits on the side of the truck facing towards the base plate. This is referred to as the load bushing or inner cushion. The double action mechanism has two cushions, one above and one below the truck, relative to the base plate. This second cushion is referred to as the steering bushing or outer cushion. The single action mechanism is older and generally is not used for skating styles requiring fine control. Most modern skating mechanisms are of the double action variety. Skateboards generally use steering and suspension mechanisms very similar to those used by roller skates, and have similar shock absorbing, steering and lateral stability requirements.
The truck typically also includes a cushion mount and a tubular stem which in higher quality roller skates is threaded to hold an adjustable pivot. The cushion mount typically has a ring-shaped area with recesses on both axial faces to position a pair of tubular cushions formed from urethane or other elastomeric material. A stud or kingpin is typically fastened into the base plate and is inserted through the ring-shaped area and through axial openings in the cushions and in many higher quality roller skates is secured with a nut along a threaded length protruding outward from beyond the cushions. In some cases a portion of the threaded length is split and the nut may have compression calibration marks for setting cushion compression as part of the skate suspension and steering adjustment. This kind of nut is called a micrometer nut and is typically locked in place with a taper-headed set screw. A ball ended stud (or ball stud) functions as a rounded pivot and is typically threaded into the tubular stem of the truck and the ball end of the stud is seated in a pivot cup, which in the prior art is typically made of rubber, elastomer, brass, steel, or a polymer such as Delrin. Frequently in high performance quad skates the ball stud can be threaded inward or outward from the truck to adjust the action of the skate steering and suspension. Prior art adjustable pivots allow skaters to set the angle of the trucks and also set the degree of preload on both the load bushing and the steering bushing. Washers and other fasteners may be used to adjust the elastic performance of the cushions. Typically the two pair of wheels and their support hardware are identical for front and back.
The truck geometry also influences skate steering and lateral stability, where major factors include the orientation of the pivot pin, the axle and the kingpin, and the angular relationship between these parts. If the axle is positioned between the pivot pin and the kingpin, the skate will have better lateral stability but less responsive steering. If the pivot pin and the kingpin are adjacently positioned and the axle is positioned out beyond the kingpin, the steering will be more responsive but the lateral stability will decrease. This geometry also tends to shorten the wheelbase, thus further decreasing overall stability. It has been found that having an approximately 45 degree angle between the pivot pin and the base plate, and also an approximately 45 degree angle between the kingpin and the base plate, yields a very responsive steering geometry, though with a consequent decrease in lateral stability. Depending on the skating style, this may be preferred.
For competitive roller skating activities such as roller derby, the skate mechanism is subjected to extreme impacts during jumps and falls, as well as the stresses of high speed skating, tight turns and the dynamic forces caused by sudden acceleration and deceleration. One particular problem with prior art skate mechanisms is wear and damage to the pivotal connection between the truck and the base plate. The simplest pivotal connection is generally a protruding portion of the truck with a rounded end, engaging a rounded recess in the base plate. As the resiliently mounted truck moves, the pivotal connection will rotate through some amount of arc, but it may also momentarily separate and then re-contact with some amount of impact, an effect known as “slap”. This will wear the joint and over time the amount of separation and slap will increase. The skate mechanism will also feel looser and less tightly controlled, and may eventually fail due to stress and impact. Additionally, slap and mechanism play will cause fatigue to the skater and may even promote joint injuries. Mechanism play can also increase the probability of sudden component failure. The impacts experienced by the skate mechanisms can cause the cushions to suffer heavy uneven wear, the pivot cups to wear and even crack, and the kingpins to crack as well. Sudden component failure can easily lead to skater injuries. Also, increasing steering responsiveness by overly loosening the resilient clamping around the trucks can lead to sudden pivot joint separation and consequent spinning of the truck around the kingpin, with skater injury being a likely result.
Prior art improvements on this pivotal connection have generally taken one of two forms. A cup formed of resilient material is inset into the base plate to receive the pivot, thus providing some degree of shock absorbing. This cup will wear over time and under extreme circumstances (which are not infrequently encountered in activities such as roller derby) may actually crack apart. Alternatively, a metal insert formed of a relatively slippery alloy such as bearing bronze and having a spherical section recess may be inset into the base plate, and a pivot having a ball end engages it. The pivot action may be further improved by threading into the truck and being pre-loaded against the metal insert. This style of pivotal connection will provide no shock absorbing but will pivot smoothly for a while. Eventually it will wear and then slap will increase.
The tradeoff between skate lateral stability and steering performance has been a source of many skate inventions too. U.S. Pat. No. 7,287,762 entitled TRUCK FOR SKATEBOARDS teaches a truck mechanism with a pin-kingpin-axle configuration in order to permit tighter turns, and incorporating the standard paired elastomeric cushions and a resilient cup to cushion the pivot pin. The '762 patent also teaches having the kingpin perpendicular to the pivot pin with the axis of each at approximately 45 degrees to the base plate, which tends to provide a highly responsive steering geometry. Also taught are a variety of angular orientations for the kingpin and pivot pin, thus affording a variety of performance styles to a skateboard.
However, the '762 patent does not teach any means for preloading the pivot mechanism for protection against static and dynamic forces, and the resilient cup provides a very limited amount of shock absorbing and historically has been prone to high wear and even splitting apart.
U.S. Pat. No. 6,547,262 entitled SKATEBOARD TRUCK ASSEMBLY teaches the use of different geometries of load and steering bushings, including a necked-down bushing for increased ease in steering. Also taught is a pivot pin mechanism comprising a pivot pin having a cylindrical section engaging a ball bearing seated in an elastomeric cup. This mechanism provides free rotary pivoting and some shock absorption for the ball bearing and pivot pin.
However, the pivot pin taught by the '262 patent primarily offers free rotation around a single axis rather than in all directions as a ball joint provides, and suffers the well known problems of the limited shock absorbing response and limited durability provided by a resilient cup. Nor is the pivot pin adjustable for preloading. Additionally, the pin-axle-kingpin geometry will provide less tight turning capability than a pin-kingpin-axle geometry.
U.S. Pat. No. 6,182,987 entitled TRUCK ASSEMBLY WITH REPLACEABLE AXLES AND BALL JOINT PIVOTS teaches the use of different geometries of upper and lower elastomeric cushions, including a hemispherical cushion engaging a socket in the truck for improved rotation and steering. An adjustable pivot pin with a ball end engaging a spherical section shock-absorbent socket is also taught.
However, the '987 patent also suffers from the problems of the limited shock absorbing response and limited durability provided by a resilient cup, even though the ball joint will provide an improvement in rotation. In addition, the pin-axle-kingpin geometry will provide less tight turning capability than a pin-kingpin-axle geometry.
A more capable and robust roller skate steering and suspension mechanism would provide a pre-loadable, adjustable, durable yet resilient pivoting connection between the skate truck and the base plate, effectively creating a third action to augment the double action skate mechanism. Additionally, the base plate portion of the mechanism would be extremely lightweight and stiff to reduce skater fatigue and increase performance, and very durable to avoid breakage during competitive skating activities. Such a skate mechanism would be usable in skateboards as well.